1. Field of the Invention
The present invention relates to a contour compensator for a carrier chrominance signal in a television, a video tape recorder (hereinafter referred to as "VTR") or the like.
2. Description of the Background Art
FIG. 1 is a block diagram showing a conventional method of generating a carrier chrominance signal in a VTR or the like. As shown in FIG. 1, a luminance signal and a chrominance signal recorded in a tape are converted into an electric signal S1 by a head 1, and outputted to a head amplifier 2. The luminance signal is a frequency modulated signal, and the chrominance signal is a low-frequency converted signal.
The electric signal S1 is amplified by the head amplifier 2, and then the frequency modulated luminance signal is removed through a low-pass filter (LPF) 3. Consequently, only a low-frequency chrominance signal S.sub.C is outputted to a main frequency converter 4.
On the other hand, a voltage control oscillator (VCO) 5 forms a PLL circuit (not shown), to output a signal S5 which is synchronous with the chrominance signal S.sub.C to a subfrequency converter 6. A crystal oscillator 7 outputs a subcarrier CS1 to the subfrequency converter 6. The subfrequency converter 6 frequency-converts the signal S5 by using the subcarrier CS1, to output a signal S6 to the main frequency converter 4. The frequency converters 4 and 6 may be multipliers
The main frequency converter 4 converts the signal S.sub.C into a high frequency range by using the signal S6, to output a signal S4. This signal S4 passes through a band-pass filter (BPF) 8 and a comb filter 9 to be outputted to the exterior as a carrier chrominance signal CCS, from which unwanted frequency components and crosstalk components are removed.
Although an ideal waveform of the carrier chrominance signal CCS is as shown in FIG. 2A, abrupt portions of the waveform are rounded by losing the high-frequency components as shown in FIG. 2B, since the carrier chrominance signal CCS is obtained through the LPF 3 and the BPF 8.
As hereinabove described, the abrupt portions in the waveform of the carrier chrominance signal CCS obtained by playing back the VTR are so rounded that turning points (contours) of colors are blurred to cause bleeding or the like.
Therefore, it has been necessary to perform contour enhancement by detecting relatively abrupt portions in the waveform of the carrier chrominance signal CCS to enhance abruptness thereof.
However, it has been difficult to perform contour enhancement of the carrier chrominance signal CCS itself, because:
(1) The carrier chrominance signal CCS is in a high-frequency range.
(2) It has amplitude and phase information.
(3) Since it is a chrominance signal, addition of overshooting for aperture control etc. cannot be performed dissimilarly to a luminance signal.
It may be considered to temporarily convert the carrier chrominance signal into a chrominance signal of the baseband for facilitating contour enhancement, without performing addition of overshooting etc. In this case, however, hue change, saturation change and the like are easily caused in re-conversion into the original carrier chrominance signal.